Concentrated selenium toner and process of making



Patented Aug. 14, 1945 CONCENTRATED SELENIUM TONER'AND raooass OF MAKINGWalter V. Wadman and Lionel D. Butcher, Rochester, N. Y., asslgnors toEastman Kodak Company, Rochester, N. Y.,

Jersey a corporation of New No Drawing. Application June 30, 1942,Serial No. 449,182

7 Claims.

This invention relates to, a concentrated selenium toner adapted to bediluted with water for use and process of making the same.

Selenium toners are well known in the photographic art. However,selenium toners heretofore used have been prepared immediately prior touse and have been in the form of dilute photographic baths. Such dilutesolutions can not be marketed. As the result of numerous experiments wehave found that the preparation of concentrated selenium toners presentsmany difliculties. Selenium is.a peculiar material insofar as its toningproperties are concerned. It is difficult to get into solution,particularly in high concentrations, and it may be easily converted intoselenium compounds having no toning properties. Also, it may beprecipitated by the presence of other materials, particularly in highconcentration. Selenium is quite similar to sulfur and it will berealized that its incorporation in toning solutions in highconcentration along with the large amounts of other necessaryingredients of a satisfactory selenium toner is a diflicult problem.

This invention has for its object to provide a selenium toner inconcentrated aqueous solution adapted to be diluted with water to form asatisfactory selenium toning bath. A further object is to provide aconcentrated selenium toner containing the selenium compound -'in stablecondition and in solution. A still further object is to provide aconcentrated selenium toner adapted to be diluted for use and in dilutedcondition adapted to form a rapid toning bath. Other objects will appearhereinafter.

These and other objects are accomplished by our invention which includesan aqueous concentrated selenium toning solution adapted to be dilutedwith water to form a photographic toning bath, said concentratecontaining a thiosulfate of a nitrogen compound and having a pH range ofabout 6.5 to 8.5.

We have found that the selenium compound having a toning action may beincorporated in the necessary high concentration when in the presence ofthe nitrogen-containing thiosulphate and at the pH value mentionedwithout precipitation of the selenium compound, or destruction of itstoning properties. The selenium compound is also preserved so that itwill exert its full tonin effect even if the concentrate is stored for along period of time, as customarily takes place between its passage fromthe manufacturer to the consumer. The nitrogen-containing thiosulfatealso contributes to the concentrated toner in otherways. It greatlyincreases the speed of toning and also prevents toning of the whiteportions of the.picture.

In the following description we have given several of the preferredembodiments of our invention but it is to be understood that these areset forth for the purpose of illustration and not in limitation thereof.

The selenium compound present in the concentrated toner is preferably analkali metal selenite such as sodium selenite. This material can beadded as such to the concentrate but it is preferred to form it therein.Thus, metallic selenium may be added to the concentrate in which casesodium sulfite is also present. A reaction takes place between theselenium and the sodium sulfite to form sodium selenite. It is desirablethat an excess of sodium sulfite be present in the concentrated toner toact as a stabilizer, or preservative. Selenic acid, selenium dioxide andother selenium compounds may be used in the concentrate instead of thesodium selenite mentioned. When these materials are used the reactionmentioned in connection with the selenium may take place, al-' thoughthis cannot be stated definitely since there are numerous substancespresent making possible several reactions.

The pH of the toning concentrate is important. If the pH of theconcentrated toner is below about 6.5, the rate of toning is rapidlydecreased and the tone qualities are inferior. If the concentrated tonerhas a pH of above about 8.5,. it will function satisfactorily as atoner. However, such a solution has the objectionable odor of ammoniaand is unstable. The pH can headjusted by the addition of acidicmaterials such as sodium bisulfite or other alkali metal bisulfite. Theacidic material should preferably have a high pH of about 4 to 6. Anacid such as aqueous sulfurous acid could be used but sulfur dioxideshould not be run into the mixture in order to acidify it since thiswill precipitate the selenium. We prefer to use sodium bisulfite forthis purpose since it will not only adjust the pH to the desired value,but also form sodium sulfite which acts as a protecting agent.

In some cases the specific nitrogen-containing thiosulfate selected willnot have th power of increasing the toning speed of the selenium; inthis case there may also be added to the concentrate an ammoniumcompound having this property, such as ammonia, ammonium chloride, urea,thiourea, etc. Examples of nitrogen-containing thiosulfates are ammoniumthiosulfate, uanidine thiosulfate and ethanolamine thiosulfate.

The necessary. constituents of the toner concentrate are present in suchhigh concentration that the concentrate can be diluted with water toseveral times its original volume to form a satisfactorily active toningbath. The amount of selenium present preferably should be about 1% to1.5%; the thiosulfate should preferably be present in amounts of 30% to45%, and the sulfite or preservative preferably in amounts of about 5 toalthough somewhat larger or smaller amounts of these materials can beused.

Example 30 grams of sodium selenite are dissolved in 300 cc. of water(125 F.); 500 grams of ammonium thiosulfate, '75 grams sodium sulfiteand 100 grams sodium bisulfite wer dissolved in another quantity ofwater amounting to 500 cc. The sodium selenite solution was then addedwith constant stirring to the second solution. The volume was adjustedto make one liter and the pH of the mixture was then adjusted to 6.98 bythe addition of sodium bisulfite. This concentrated solutionprecipitated none of its constituents during keeping over a substantialperiod of time. For use it is diluted with three parts of water at about70 F. and will satisfactorily tone in the very short time of two to fiveminutes. Washing with water should follow the toning.

The concentrated toner can be used for the same purpose as seleniumtoners heretofore prepared, thus it may be employed to tone photographicpapers of various types such as Velox, Azo, Portrait proof, and otherphotographic papers containing silver chloride, silver bromide, ormixtures of such light sensitive substances which have been exposed anddeveloped. Toning treatment is preferably applied to the developed imageimmediately after fixing and before drying of the prints. However, itmay be applied to dry prints or photographic images in other stages ofpreparation.

What we claim is:

1. An aqueous concentrated selenium toning solution adapted to bediluted with water to many times its original volume to form aphotographic toning bath, said concentrate including an aqueous'solutionof a selenium compound hav ing a toning action, and anitrogen-containing thiosulfate, and having suflicient acidic substancepresent to give a pH range of about 6.5 to 8.5, the selenium compoundbeing present in an amount suflicient to give between about 1 and 1.5%selenium content, the nitrogen-containing thiosulfate in an amountbetween about 30 and 45% and all of the constituents being substantiallycompletely dissolved in the water and being present in such highconcentration that the concentrate can be diluted with water equal tomany times its volume to form a satisfactory toning bath.

2. An aqueous concentrated selenium toning solution adapted to bediluted with water to ma y times its original volume to form aphotographic toning bath, said cancentrate including an aqueous solutionof a selenium compound having a toning action, a preservative, anitrogencontaining thiosulfate, and an alkali metal bisulfite, andhaving sufficient acidic substance present to give a pH range of 6.5 to8.5, the selenium compound being present in an amount suflicient to givea selenium content of between about 1 and 1.5%, the nitrogen-containingthiosulfate in an amount between about 30 and 45% and all of theconstituents being substantially completely dissolved in the water andbeing present in such high concentration that the concentrate can bediluted with water equal to at least three times its volume to form asatisfactory toning bath.

3. An aqueous concentrated selenium toning solution adapted to bediluted with water to form a photographic toning bath, 'said concentratecontaining about 1 to 1.5% selenium, about 30 to 45% of anitrogen-containing thiosulfate and about 5 to 10% of a soluble sulfite,and having sufficient acidic substance present to give a pH range ofabout 6.5 to 8.5 the constituents being substantially completelydissolved in the water.

4. An aqueous concentrated selenium toning solution adapted to bediluted with water to many times its original volume to form aphotographic toning bath, said concentrate including an aqueous solutionof an alkali metal selenite, an alkali metal sulfite, an alkali metalbi-sulfite, and a nitrogen-containing thiosulfate and and havingsufficient acidic substance present to give a pH range of 6.5 to 8.5,the alkali metal selenite being present in an amount sufiicient to givebetween 1 and 1.5% selenium content, the nitrogen-containing thiosulfatein an amount between about 30 and 45% and all of the constituents beingsubstantially completely dissolved in the water and being present insuch high concentration that the concentrate can be diluted with waterequal to at least three times its volume to form a satisfactory toningbath.

5-An aqueous concentrated selenium toning solution adapted to be dilutedwith water to many times its original volume to form a photographictoning bath, said concentrate including an aqueous solution of aselenium compound having a toning action, an alkali metal sulfite, analkali metal bisulfite, and ammonium thiosulfate, and having sufficientacidic substance present to give a pH range of 6.5 to 8.5, the seleniumcompound being resent in an amount sufiicient to give between about 1and 1.5% selenium content, the ammonium thiosulfate in an amount betweenabout 30 and 45% and all of the constituents being substantiallycompletely dissolved in the water and being present in such highconcentration that the concentrate can be diluted .with water equal toat least three times its volume to form a satisfactory toning bath.

6. An aqueous concentrated selenium toning solution adapted to bediluted with water to form a photographic toning bath, said concentrateincluding as initial constituents an aqueous solution of about 30 gramsof sodium selenite, 7 grams of sodium sulfite, grams of sodiumbi-sulfite and 500 grams of a member of the group consisting of ammoniumand guanidine thiosulfate, and having a pH of about '7, saidconstituents being contained in 1 liter of solution in the amountsindicated and being substantially completely dissolved therein.

7. The method of preparing a concentrated selenium toner which comprisesdissolving a selenium compound having a toning action in water to form afirst solution, dissolving a nitrogen containing thiosulfate, a solublesulfite and a bisulfite in water to form a second solution, adding thefirst solution to the second with stirring and adiusting the pH of themixture to between about 6.5 and 8.5 by incorporation of an acidicsubstance the selenium compound being present in the final mixture in anamount sufficient to give a selenium content of between about 1 and 1.5%and the nitrogen-containing tgiosulfate in an amount between about 30and 4 WALTER V. WADMAN. LIONEL D. BUTCHER.

